Cereal is not a soup because it does not give you warm feelings inside.
It’s better to think of cereal as bread or toast with milk or water poured on top. It doesn’t have the same feeling inside as eating soup because it doesn’t affect your body in the same way. Eating cereal may be an alternate breakfast choice, but it doesn’t affect your stomach temperature in a way that makes you feel content like a bowl of soup does. When you eat something that’s hot, your stomach feels full and happy whereas when you eat an icy-cold cereal with ice cold milk, often times the stomach does not fill up easily and can lead to hunger pains 30 minutes later.